In a large nonstick saucepan, saute the onion in oil for 10 minutes or longer (until carmelized). Add celery, carrots, and garlic; cook 10 minutes longer.
Add the beans and saute a couple of minutes.
Pour in enough water, chicken broth, or a combination of both to cover beans by about an inch ot two.
Stir in tomato paste, brown sugar, salt, and pepper. Bring to a boil. Reduce heat; cover and simmer for 1 hour (at least) or 2 hours for dried beans (or until tender).
Add salt and pepper to taste. You can add chopped chicken, spinach, or cooked pasta.

Grated parmesan cheese helps pull all the flavors together.
This soup freezes well and can easily be reheated by stove or microwave.